The present invention relates to an electric supply unit, a sputtering installation as well as a method for reducing arcing during sputtering, and further a fabrication method.
The present invention builds on the following problem. The findings gained according to the invention, can be generally applied for HF-supplied sputtering processes.
During magnetron sputtering of ITO layers of oxide targets and supply of the plasma discharge, combined of HF and DC, the development of arcs is sporadically observed. This is not surprising, for the occurrence of such arcs is known in the case of DC sputtering of electrically poorly conducting materials, be that for sputter etching or for sputter coating. Several different approaches are known in order to avoid the development of arcs during DC sputtering, which could considerably damage workpieces during sputter etching as well as during sputter coating. For example the DC supply is superimposed by an HF supply component or work is carried out through operating point stabilization in so-called intramode or the DC supply is chopped so that the plasma discharge path is intermittently short-circuited across a relatively low-ohmic current path, while the DC supply is cut out.
It is thus all the more surprising that, in spite of the HF supply superimposed on the DC supply, said arcing was observed and an arc once developed continued to burn even if, according to experience from DC-supplied sputtering technology, the DC supply component had been deactivated.
The present invention builds on the surprisingly resulting task of suppressing the arc development during HF sputteringxe2x80x94generally sputter coating or sputter etchingxe2x80x94at least so fast that the workpiece being worked is not damaged.
For this purpose, a supply unit of the type described in the introduction is proposed, which is developed according to the invention. Consequently, the supply unit according to the invention is developed such that the HF supply of the sputter plasma discharge is briefly deactivated.
In a first preferred embodiment of the supply unit according to the invention the switching unit controlling the deactivation comprises a control input, which is operationally connected with the output of an arc detection unit. It thereby becomes possible to deactivate the high-frequency supply of the plasma discharge immediately when an arc is developing.
The HF generator provided for the supply comprises in the conventional manner an electric supply unit which, for example, converts an input-side mains voltage into a DC supply voltage for the succeeding HF oscillator.
In a preferred embodiment of the unit according to the invention the switching unit provided for the deactivation according to the invention of the high-frequency supply succeeds said supply unit internal to the HF generator, i.e. it is disposed between the output of said supply unit and that of the HF generator. This can take place succeeding said generator supply unit up to the output side of an impedance matching unit provided conventionally and, in the present case, considered to be part of the generator.
In a preferred embodiment of the supply unit according to the invention equipped with an arc detection unit the latter comprises a DC potential measuring unit, whose output is operationally connected with the input of a preferably adjustable threshold value detection unit, whose output, in turn, acts as the output of the arc detection unit.
It is known that even with the exclusive HF supply of a plasma discharge, DC potentialsxe2x80x94DC potential drops across the electrode dark spaces, essentially constant DC potential along the remaining plasma pathxe2x80x94are generated along the plasma discharge path, whose values change detectably when a low-ohmic arc path is generated.
In a further preferred embodiment of the supply unit according to the invention the deactivation time of the HF supply is maximally 40 xcexcsec., preferably even maximally 30 xcexcsec.
It is thereby attained that, on the one hand, an arc in the process of developing is extinguished or, as will yet be explained, cannot even form and simultaneously a stable discharge is immediately continued in operation.
In a further preferred embodiment it is attained, in particular when the deactivation of the HF supply triggered by arc detection is provided, that, in addition to the previously described rapid switching in again, after the detection of the arc development, the HF supply is rapidly switched out such that the arc which is in the process of developing cannot fully develop. This is attained thereby that the time interval between arc detection and switching-out of the high-frequency supply is maximally 50 xcexcsec, preferably maximally 30 xcexcsec.
In a further preferred embodiment the switching unit provided according to the invention is developed in the manner of a monostable unit. Triggered by a detection signal at the output of the provided arc detection unit, the high-frequency supply is thereby deactivated for the preferably adjustable time interval, and subsequently is again switched in. If subsequently, acquired by the arc detection unit, measured values indicating arcs continue to be present, the HF supply is again deactivated. Controlled by the arc detection, a repetitive switching in and out of said supply occurs, until the arc detection unit no longer triggers the switching-out of the supply. But the supply switch-out remains to be dependent on the detection of at least one arc in the process of developing.
But in a further preferred embodiment this is circumvented thereby that in free-running mode the HF supply is repetitively deactivated for brief periods of time.
In a further preferred embodiment of the supply unit according to the invention, in addition to said HF generator, a DC generator is provided, whose output signal is superimposed onto that of the HF generator.
The DC generator further preferred comprises also a controlled switching unit, by means of which the DC supply signal can be deactivated for a brief time.
If, for the triggering or deactivation of the HF supply an arc detection unit is provided, the latter can also drive the deactivation of the DC supply. It is understood that this can also take place directly or thereby that in mutual time dependence, as will yet be explained, HF and DC supply can be deactivated or switched in.
At the supply unit according to the invention the mutually dependent time driving of the provided controlled switching units takes place such that the DC supply is deactivated before the HF supply. The HF supply is switched in again before or after the DC supply, preferably after.
The supply unit according to the invention is realized in a preferred embodiment utilizing a DC supply of type xe2x80x9cPinnaclexe2x80x9d by the firm Advanced Energy.
Preferred embodiments of the sputter installation according to the invention are specified in the claims as are preferred embodiments of the method according to the invention.
The present invention, furthermore, relates to a fabrication method, by means of which the resulting sputteredxe2x80x94sputter-etched or sputter-coatedxe2x80x94structural components can be produced with increased quality or with significantly reduced rejects due to at least strongly reduced effects of arcs.